Tagged: web rendering week

So I’m back home now. The flight home was a bit shorter, about two hours, thankfully. Interestingly enough I feel more jet lagged now that I’m home then I was in Taiwan. I’ve heard that going east is worse then going west, so that might be the case for me right now. The rest of the rendering week, after I blogged last Tuesday, was just as awesome as the first part.

How Gecko Does X

I got to sit in on a lot more talks about “How Gecko does X” — like how the graphics engine works, how the layout system works, and my favourite in particular, how cycle collection works. Kyle Huey did an excellent job explaining how the Gecko cycle collector works. He gave us this paper as forward reading about it (it’s a little dense, but definitely worth reading). I’ll try to do a blog post in the future on what I learned/will learn about it.

David Baron and Adam Roach also gave an awesome talk on how the W3C and IETF work. WEBVTT is my first major exposure to open specifications that I’ve had and so I’ve been interested in all the hows/whats/whys of open specifications and the politics behind them.

Initial WEBVTT Support

It wasn’t all fun and games over in Taiwan though. We were also doing a lot of work. We finally got bug 833385landed near to the end of the week. This means that we have support for all the new DOM elements that WEBVTT introduces such as: HTMLTrackElement, TextTrack, TextTrackList, TextTrackCue, and TextTrackCueList. We ran into a random inexplicable bug when we were doing full tries on the code, just before landing it. Ralph and I went to work debugging it (had to use an ASAN build) and we ended up discovering that it happened in a very rare situation where the cycle collector nulls out the HTMLMediaElement’s TextTrackList member while the HTMLMediaElement is still alive. This results in a situation where HTMLMediaElement::FireTimeUpdate() is called just before it is about to be deleted and since we weren’t doing null checks on the call to TextTrackList::Update() we would crash. After we got that fixed we were all green.

That leaves just bug 833382 left before we get initial support for WEBVTT. It was going well last week and we got an r+ from Chris Pearce. Now we just need an r+ from Boris and we should be good to go. It might take a few more rounds of review before that happens, but I’m optimistic we will be able to get this landed within a week or so.

One of the major problems I was having in Taiwan was trying to get a clean diff for 833382. The problem centered around the fact that up until now, mainly in my previous open-source class, we decided to use a git branch as a main point of ‘integration’. We’ve all been working off this branch for a while. The history of this branch has been so ridiculous and the code necessary for 833382 depends on so many other parts of the code that have been touched by, well everyone, that it was pretty much impossible for me to do a clean diff or even get a good rebase. To rebase this beast I would have had to go through 150+ commits, each having merge conflicts… So I ended up just making a clean branch off master and manually moving all the code that I needed over to the new branch and doing a diff like that. I’ll probably be staying away from these kinds of ‘integration’ branches in the future in order to ensure that my repo history can be more linear. Easier to get diffs that way.

The other thing I’ve been dealing with in the last few days is some code we landed back in February that was spotted to not be up to par by Boris. The issue is with some of the CSS selectors that we are using to style WEBVTT text — namely, we are using slow CSS selectors which is bad. This is the first that I’ve heard about some CSS selectors being slower than others, although that’s not suprising as I’m not super-super knowledgeable about CSS. Mozilla even has a page devoted to this that you can check out here. Ralph and I put together a patch yesterday to deal with this which will land today most likely. I’ll have to update 833382 to reflect those changes today as well.

CSS Parser Hacking

I also sat in on the vertical-text layout meeting as it is of particular interest to WEBVTT. WEBVTT requires the ability to have vertical-text and so far in Gecko we don’t have this. Apparently vertical-text has been kind of a thorn in the side of the layout team for a long time as it’s been particularly hard to implement. However, there is a major push now to get it done, so that’s great. In accordance with this Daniel Holbert asked me if I wanted to do some stuff for vertical-text in the CSS parser, I accepted and got my first layout bug! So I’ll be hacking around in the CSS parser and layout section of Gecko more in the future, hopefully.

WebMaker

Dave also told me the other day that he’s figured out an area of WebMaker that I can start contributing to, so I’m excited about that. I’ll be starting in about two weeks on this. I’ll most likely be splitting my time like 70/30 or something like that for WEBVTT and WebMaker. We talked briefly about it and so my understanding isn’t 100%, but what I got from our talk is that I will be implementing a kind of wrapper around an HTML5 video element that will allow Popcorn Maker to be able to work with it. From my understanding Popcorn Maker works with many different video formats/sources and so it needs a uniform interface to work with all these different videos. That’s where the wrapper comes in. It allows Popcorn Maker to work with many different video formats and sources without worrying about the particulars. However, all this might be completely wrong as I might have misunderstood some things from our brief conversation… So don’t take my word for it! At any rate I’ll do another blog post about it when I get more information.

After a ridiculously long flight, 24 hours in total including airport time, we finally arrived in Taiwan, met up with Daniel (IRC:dholbert) and Seth (IRC:seth) and were on our way to the hotel in a cab. The plane ride was pretty good. Uneventful… just super long.

Taipei 101 building

It’s now Wednesday and it’s been an awesome and eventful week. I’ve been meeting tons of Mozilla devs and learning a lot. We’ve also been working hard on landing that initial support for WEBVTT I was talking about in my last blog post.

Sunday I was kind of jet lagged so I took a quick power nap and woke up for dinner which we ate at the Tapei 101 building (formerly the tallest building in the world). Dinner was like 15 courses? Pretty full after that.

After sleeping Sunday night I was pretty much jet lag free… I was kind of surprised as I’ve heard it’s really hard to deal with for some people. My first experience with it was kind of a non-issue. It’s probably because I’m used to sleeping late anyways… so really I just corrected my schedule to what’s normal for most people.

This week is pretty much a week where all the Web Rendering people can get together and work and talk face to face. There’s been a lot of meetings, some of which I’ve sat in on, that are super interesting and informative. Robert (IRC:roc) gave an excellent talk on the working culture at Mozilla which has really reiterated to me again how awesome the Mozilla working culture really is and how different it is from other companies. The talk touched on openness at Mozilla, code review, software quality, and module ownership vs. Mozilla’s managerial structure among many other things.

On the way to the office

Aside from working on initial WEBVTT support I’ve also been getting reacquainted with the specification as it’s changed a lot since I last looked at it, going over all the bugs that we currently have for WEBVTT in order to get some kind of an idea of what we need to do next, and engaging in a lot of discussions about what we think the WEBVTT spec needs to improve on or change. This is great as when I get back to Toronto I’ll have a better plan of what needs to be done and how we are going to do it.

I’m also learning a ton about different areas Gecko that I didn’t know about before just by listening to and talking to others. Overall I’d say I’ve learnt way more then I could ever hope to do in the same amount of time sitting on IRC chatting with people.

One other thing I’m looking forward to is a talk on the cycle collector that Kyle (khuey) is going to be giving tomorrow. The more I try to work with and use cycle collection the more I want to understand it. Hopefully I can walk away from the talk with a better understanding of how it works.

Here are some assorted pictures of the Mozilla Taiwan office. It’s pretty brand spanking new. The office space they have us working in was actually just finished before we got here and they had to push the contractors to get it done early. It’s right across from the Bloomberg office here in Taipei as well as some other cool places. It’s literally 30 seconds from Taipei 101, so it’s right in the downtown core of the city.

Stinks that I won’t have enough time to check out many other places in Taipei as work is taking up most of my time. Taiwan isn’t the place I thought I would visit first when traveling to Asia, or even a place I would visit, but it’s definitely on my list of places to come back to.